In the field of Computer Vision, the technique of structure from motion (SfM) refers to the process of constructing a point cloud that estimates three-dimensional structures from a set of two-dimensional images, such as a sequence of two-dimensional images of a scene taken from different perspectives. The resulting reconstructed, three-dimensional image is created in a relative coordinate system (e.g., an arbitrary world coordinate system (WCS)) that satisfies the established image geometry but without knowledge of its relationship to a fixed, earth-based coordinate system. The problem of obtaining a geoaccurate three-dimensional point cloud has received little attention in the literature, largely due to a perceived barrier between the fields of Computer Vision and traditional photogrammetry. It has been proposed that the relative model from the SfM process may be manually placed into a desired fixed, earth-based coordinate system using ground control points (GCPs). Attempts have also been made to alter the default initialization of the adjustment algorithm in SfM using geotags and vanishing point estimates or by using metadata containing sensor position and orientation information. Others have proposed geo-spatial registration of imagery.
A major shortcoming of many geo-spatial registration methodologies is the use of an external digital elevation map (DEM) to achieve accurate geolocation. Use of geotags as prior geolocation information in the adjustment process has been demonstrated to obtain geoaccurate ground-level reconstruction. However, attempts at a similar process for airborne imagery resulted in undesirable global translation due to drift in the algorithm employed. Using external position and/or orientation information as initialization parameters introduces undesirable error into the adjustment process of SfM, which may produce larger inaccuracy for long-distance image capture, e.g., from airborne or satellite platforms. Accordingly, there remains a need for techniques for obtaining geoaccurate image-based three-dimensional scene reconstructions in the absence of ground control points or an external DEM.